2019年3月13日 · The sizing and number of VLFs inside of a transaction log can be affected by a number of factors. SQL Server should not have an excessive number of Virtual Log Files (VLFs) inside the Transaction Log. Having a large number of small VLFs can slow down the recovery process that a database goes through on startup or after restoring a backup.

2019年3月23日 · Last week, a team mate (Luis Canastreiro) pointed out that he wasn’t getting that message during recovery on a database with over 1000 VLFs. Well, it seems that has indeed changed in RTM and the message now shows when you have over 10000 VLFs. So here is how I verified this. I created four databases: --Create DBs USE [master] GO

2019年3月23日 · Anyhow, a few months back I knew of a case where a database had over 1.2 million VLFs, and it took a very long time to recover when a restart was performed on the instance. More recently I as made aware of a database with over 930k VLFs. Thankfully, the database owner wanted to preemptively deal with the situation.

2019年3月15日 · Even though the VLFs were still considered active, they were able to be reused since they were part of the previous transaction log backup. We noticed that in a mirroring or Availability Group scenario, Lazy Log Truncation marks the VLFs for truncation, but it does not actually truncate the log unless those VLFs are necessary.

2023年3月13日 · You need to periodically check AG databases to make sure they do not have too many Virtual Log Files (VLFs) which can severely impact redo process of the secondary. Diagnosis and corrective steps are discussed in the article Too Many Virtual Log Files (VLFs) Can Cause Slow Database Recovery .

Too Many Virtual Log Files (VLFs) Can Cause Slow Database Recovery First published on MSDN on Feb 22, 2012 The Transaction Log of a SQL Server database is composed of one or more physical files.

2019年3月23日 · A list of all the databases with the count existing and used VLFs, the total and used log size, and finally the average VLF size within each database. With more detail, a list of all the recorded growth iterations that happened in each database and the VLF size per spawn, ordered by growth iteration (actually MinLSN).

2019年3月23日 · I repeated the transaction (after backing up the log to clear it) and disaster struck again, this time with 5000 used VLFs (status 2), and the same message was recorded. I also ran database SET OFFLINE / SET ONLINE with either 5000 used VLFs and only 1 used VLF, and still the message got into the Errorlog. So thank you Kalen for mentioning it.

2019年1月15日 · As a result, the log will have several 1000 to several million VLFs (you can read more about VLFs in Transaction Log Physical Architecture ). The first phase of recovering a database is called discovery where all the VLFs are scanned (in serial and single threaded fashion) before actual recovery starts. Since this happens much before the ...

2019年3月23日 · For the scope of this blog post, the concepts that need to be conveyed are that SQL Server allocates log space in logical sections called Virtual Log Files (VLFs) within each physical log file, and depending on the logging level of that database, there are several actions that trigger something called log truncation, which is the action of ...